1. Field of the Invention
This invention relates to the area of substrate processing systems and more specifically to a system and apparatus for transferring a substrate to a processing chamber and subsequently processing a substrate under sub-atmospheric pressure within a process chamber.
2. Description of Prior Art
Flat substrates, such as round silicon wafers, rectangular glass panels, round, rectangular and square ceramic plates and optical grade crystalline substrates are commonly used for the manufacturing of many useful devices such as integrated circuit (IC), flat panel display, optical, electro-optical, sensor and micro-fluidic devices. In many cases, these substrates are processed within single substrate processing-chambers. Substantially automatic transport of substrates into the process chambers and out of the process chambers is commonly practiced with a variety of useful different designs and a variety of useful wafer-handling systems architecture. Substrate handling systems significantly add to the size and cost of the processing apparatus. Accordingly, it is a common practice to exploit substrate handling and transport systems to support multiple single substrate chambers. Additionally, systems configurations with multiple single substrate processing chambers are advantageously exploited in many technologies to conduct sequential and integrated substrate processing wherein a sequentially processed substrate benefits substantially from the short delay between sequential processing and the ability to maintain controlled ambient during substrate transport from one process chamber to another, therefore substantially suppressing the adverse impact of ambient contamination.
One prominent example of such crucially integrated sequence of substrate processing is the deposition of copper barrier and copper seed film stack commonly implemented in semiconductor fabrication technology. Accordingly, silicon wafers are processed to grow a thin barrier layer in a first process chamber and subsequently quickly transported, under vacuum or controlled inert ambient, to a second processing chamber where a thin copper seed layer is formed over the previously formed seed layer. The performance of the copper barrier-seed stack predominantly depends on the quality of the interface between the barrier layer and the copper layer. The quality of this interface is predominantly improved by minimization of barrier layer surface contamination and oxidation related to the ability of integrated multiple substrate wafer processing systems to minimize the exposure of the wafers to possible contamination during wafer transport between the first processing chamber and the second processing chamber.
In an another prominent example, fabrication of flat panel display Organic Light Emitting Diode (OLED) devices crucially relies upon a series of 5-7 sequential fabrication process steps that must be carried within the processing system with extremely minimized exposure to moisture and other contamination sources during substrate handling between subsequent chambers and related processing steps.
Many commercially available processes such as chemical vapor deposition (CVD), etching, physical vapor deposition (PVD) or atomic layer deposition (ALD) are implemented at controlled ambient at the sub-atmospheric pressure range. Substrate transport is typically carried at vacuum or otherwise low pressure of inert ambient. During process execution, the process chambers are completely enclosed and pressure-sealed from the substrate-handling chamber. After process completion (or before process starts), the substrate is removed out of (or into) the process chamber without venting it to atmospheric pressure, such that low pressure and isolation from the ambient is maintained.
To facilitate the substrate transport and processing, processing systems are equipped with substrate translation means, substrate placement means and with volume partition means.
Substrate handling is practiced with a variety of robotic translation and rotation stages that are capable of moving a substrate in a certain plane. Many different devices are suitable and known to those who are skilled in the art including simple linear stages, simple rotation arms, rotation-translation robots and multiple-axes rotation-based robots.
Substrate placement refers to the removal of a substrate from a station and mounting that substrate over a substrate handling member and to the reversal operation of dismounting a substrate from a substrate handling member and subsequently mounting that substrate on a station. Station refers to a variety of processing and support chambers such as a load-lock station, an alignment station, processing stations, cleaning stations, a pre-heating station, a cooling station, pattern delineation stations, a bakeout station, post processing treatment stations, an outgasing station, etc. Substrate placement members comprise means for substrate exchange between the station and the substrate handling member such as a fork-like end-effector mounted on the substrate handling member and matching lift-pins or lift-fingers mounted on the station. substrate exchange requires vertical translation of the substrate. Many useful arrangements are successfully implemented and are known to those who are skilled in the art.
Volume partition is practiced to isolate stations during processing or otherwise when ambient conditions at different stations are not compatible, such as, for example, when a load-lock station is vented to atmospheric pressure. Typically volume partitions accommodate the basic architecture of the processing system and the substrate-handling member. For example, a planar partition, such as a slit-valve, is commonly practiced in the art wherein a substrate transport path is substantially linearly defined, when the partition is opened. A channel shaped as a horizontally oriented slit is formed in the wall of each chamber to facilitate a substrate transport port. The system further includes a substrate handling member with linear translation means such as a linear-rotation, linear-linear, linear-linear-rotation or a multiple-axes rotation robot. Multiple chamber systems of that design devote a significant space to enable the robot to align parallel to the linear access paths of different chambers. One of many such useful systems is described by Maydan et al. in U.S. Pat. No. 4,951,601. Planar partitions with horizontal substrate transport plane are typically implemented with the partition vertical to both the substrate transport plane and the substrate transport path to minimize partition size and related process chamber asymmetry. When more than one substrate transport path is necessary, the processing system implements a planar partition for each path.
In yet another, less common, example, perimeter volume partitions enable unobstructed access to a station when the partition is substantially opened. Substrate handling with a single axis rotation arm complements the system, although more sophisticated substrate-handling members are also suitable. One of several such useful systems in described by Kawasaki et al. in U.S. Pat. No. 5,007,981. Perimeter partitions are typically designed to be substantially vertical to the substrate-handling plane.
Optimum process chamber geometry dictates substantial similarity to the shape of the substrate. At the same time optimized flow path for process gasses commonly dictates that substantially sharp corners must be avoided. Accordingly, process chamber geometry should substantially replicate the shape of the substrate with provisions for round corners. For example, round geometry is most suitable for round substrates while round corners rectangular geometry best accommodates rectangular substrates.
Current implementation of planar partitions, or slit valves, conventionally employs a flat design which does not interface well with the symmetry of round process chambers. As a result, a substantially large cavity is created to adapt the round inner wall shape to the flat slit valve. This inevitable cavity breaks the symmetry of the round process chamber with adverse impact on the symmetry, uniformity and consistency of various process elements, such as flow, plasma field, pressure and chemical transport. In addition, the parasitical cavity acts as a “dead space”, creating flow turbulence that notoriously generates particles. Such dead-space cavities are particularly detrimental to the performance and optimization of atomic layer deposition (ALD), an emerging cutting edge process technology. The extent of the dead-space cavity impact on performance grows as the proportional area of the cavity compared to the chamber area is increased. Round process chambers utilizing slit-valves for volume partition were therefore forced into larger diameter chambers to create substantial separation between the substrate and the asymmetry source. Therefore, slit-valve-related asymmetry imposes an inevitable increase in chamber size. Additional process system increase emerges from the need to dedicate substantial space for the substrate-handling member to maneuver from one linear path through one planar partition into another linear path through another planar partition. For example, a large transport chamber is commonly used to accommodate a robot, linear substrate pickup, substrate and robot rotation and substrate placement. For example the system described in U.S. Pat. No. 4,951,601. Substrate transport chambers contribute substantially to the overall size of the processing system. With the increase in substrate size yielding substantially more devices per substrate and the trending of many industries into short product lifetime, fewer completed substrates and therefore fewer process chambers per system are necessary. Unfortunately, the relative impact of substrate process chambers on the overall size and cost of the processing system increases as the number of process chambers per system decreases making planar volume partitions such as planar slit-valves less favorable.
Perimeter partitions can be shaped to the optimum flow geometry and advantageously eliminate the adverse asymmetry effect. Unrestricted substrate handling within the substrate transport plane eliminates the need for a dedicated substrate-handling chamber with potentially much improved utilization of system area as well as substantially simplified substrate handling. However, despite these indisputable advantages, perimeter partitioned systems continue to be unpopular. Unfortunately, perimeter partitions also enhance problems that are inherent to volume partitions.
Most problematic, as well known to those who are skilled in the art, is the integrity and the cleanliness of the partition seals and related crevices. Crevices are inherently created when partitions are operated to enclose the chambers and relate to the surfaces between the moving part of the partition, typically defined as the “slide” and the stationary part of the partition typically referred as the “housing”. As well known in the art, process chamber contamination and failure are significantly driven by the growth of undesired films and/or accumulation of contamination at exposed crevices between the slide and the housing, as well as the deterioration of the seals by exposure to harsh chemical and/or plasma environment. Unfortunately, perimeter volume partitions typically introduce at least four times longer seals and related problematic slide-housing gaps.
In an attempt to reduce the adverse impact of seal related deterioration, the prior art utilized a vertically movable stage to elevate the process space between a process chamber top and a substrate holder substantially above the seals plane. Unfortunately, this prior art improvement does not completely resolve the problem, in particular, in the case of deposition processes. Therefore, further improvements could only be driven by substantially spacing the perimeter partition away from the process with a related significant chamber area increased.
Perimeter volume partition with protected seals was taught by the inventor of this invention in US patent application number 2003/0180458 and related applications. Accordingly, an atomic layer deposition (ALD) apparatus and method are provided wherein the seals of a “perimeter slot valve-(PSV)” are located within a small volume compartment of the process chamber space, named “DGIC” having a perimeter flow restriction at the inlet and a perimeter flow restriction at the outlet and an inert gas plenum for introduction of inert gas into the DGIC. This apparatus is suitable for process method wherein a substantially high flow of inert gas into the DGIC during the introduction of process reactive gas into the process chamber is useful as described in detail in US patent application number 2003/0180458. Accordingly, the seals of the PSV are substantially protected from contact with the reactive chemicals. As a result, a small diameter PSV apparatus was successfully implemented for a substantially small process chamber footprint with exceptional protection from seal-deterioration and contamination. However, the PSV apparatus of US patent application number 2003/0180458 is specific to the synchronously modulated flow and draw ALD (SMFD-ALD) method and does not provide a seal protected perimeter volume partition apparatus with easy application to other methods.
In addition, chambers defined with perimeter partitions lack the necessary wall area where essential accessories such as pressure gauges, pressure switches, electrical feeding ports (electrical feedthrough), sensors (such as temperature measurement, end-point detection, etc.), feeding ports, view ports, pumping ports, residual gas analyzers, feeding ports for in-situ cleaning gas, to name a few, are typically communicated with the chamber space through the chamber wall. Process chambers typically have minimized usable space at both the top and the bottom ends. The top end typically hosts process gas delivery members and is inherently unsuitable to communicate the accessories listed above with the process space. The bottom end is typically substantially crowded with a cumbersome substrate placement member leaving only very limited unoccupied area. In fact, many prior art implementations of substrate placement members required that vacuum pump ports were relocated from the bottom face and placed at the chamber walls. Accordingly, conventional substrate placement members leave very limited unoccupied area at the bottom of process chambers that is substantially insufficient for relocating the above listed essentials. Substrate holder elevators that were used to alleviate seal deterioration in the prior art of perimeter partitioning, as described above, further reduce the unoccupied area at the bottom end of the process chamber. Inevitably, this situation imposes an undesired chamber area increase to provide additional necessary space at the bottom end of the chamber.
A perimeter partition valve as practiced in the prior art is illustrated in the SHUT position in FIG. 1a. Accordingly, system volume is confined by a top plate 102, a bottom plate 104 and a system wall (not shown). A process chamber 100 includes lid 106 wherein process gasses are introduced into a gas distribution device 110 through conduit 108 and are further distributed through gas dispersion member 112. The chamber includes means to support a substrate 116 such as a heated chuck 114. The bottom face of the chamber 118 is predominantly crowded with substrate placement member 122. For example the substrate includes three pins 124 (only one shown) arranged on a circle at respective 120° from each other, as commonly practiced in the art. Perimeter partition valve 150 includes an L-shaped slide 152, top perimeter seal 154, bottom perimeter seal 156, bonnet 160, guides 162 and actuators 164. Seals 154 and 156 are made from a suitable elastomer such as Viton or Kalrez or other equivalent compounds. When perimeter partition valve 150 is SHUT seals 154 and 156 are pressed against sealing surfaces 166 and 168, respectively, to pressure seal the internal space of chamber 100. Three or four actuators 164 are conveniently arranged to actuate the slide between a SHUT position (FIG. 1a) and an OPEN position (FIG. 1b). When the perimeter partition valve 150 is actuated to the OPEN position (FIG. 1b) the substrate chuck 114 is accessible from 360° directions through perimeter slit 130. The substrate 116 is levitated by pins 124 (one out of three shown) to create gap 140 between the substrate 116 and the chuck 114 which is suitable for the insertion of a wafer handling end-effector (not shown). During processing, perimeter crevices 126 and 128 at the top and the bottom seal areas, respectively, are exposed to the process ambient resulting in unacceptable deterioration and contamination and overall inferior performance. Additionally, the bulky substrate placement member 122 occupies most of the area of bottom face 118 living very limited space 120 available for process and chamber accessories. As described above, perimeter partitioned chambers must accommodate process and chamber accessories at the bottom face of the chamber.
There is a need in the art to protect the seals of perimeter partition devices to avoid process chamber deterioration and contamination and to enable optimum perimeter partition apparatus with minimized process chamber and processing system area. Complementary, there is a need for improved substrate placement members and mainly to drastically reduce the area that these members obstruct at the bottom of process chambers and to enable mounting of chamber accessories and pumping ports, at the bottom end of the process chamber.